1. Field of the Invention
This invention relates to the field of chemical processing, and more particularly to processing crude vegetable oil.
2. Description of the Related Art
Crude vegetable oils predominantly contain triglycerides along with some impurities such as free fatty acids, phospholipids, etc. These impurities are typically removed from crude oil by vegetable oil refining process. The first step in the refining process is degumming where the oil is treated with aqueous acid solution to remove both hydratable and non-hydratable phospholipids. These phospholipids are separated from the oil by centrifugation and are commonly known as wet gums. Wet-gum is a dark brown to blackish in color, highly viscous product comprising of phosphatides, water, triglycerides, and free fatty acids. The degummed oil is then treated with aqueous alkali (typically sodium or potassium hydroxide) in order to remove the free fatty acids. The alkali reacts with the free fatty acids present in the crude glycerides to form soap. The soap and other solid impurities are separated from the refined oil by centrifuging and are generally known as “soapstock” or “foots”. The soapstock obtained from this process is known as degummed soapstock and typically contains vegetable oil, water, soap, and traces of phospholipids. Alternately, in some current oil refineries the phospholipids and soapstock is removed simultaneously. The soapstock from this alternate process is known as gummed soapstock and typically contain vegetable oil, phospholipids, water and soap. Soapstock is alkaline in nature due to the presence of unreacted alkali. The refined oil is further processed.
Both wet gums and soapstock have commercial value as a source of fatty acids. Fatty acids can be recovered from wet gums and soapstock by hydrolysis. Wet gums are currently being sold as a raw material for lecithin production and for animal feed blending. Wet-gum contains phospholipids mostly phosphatidylcholine which is necessary for mobilization of fat out of the liver and also improves breeding performance and milk production of an animal. The wet gums can be dried using an evaporator to a low moisture product known as dry gums. The wet gums and dry gums products although nutritionally desirable and abundantly available in the market find limited application in feed due to their handling and storage difficulties.
Fatty acids can be recovered from soapstock as a valuable product. A product high in fatty acid content (generally about 55-65% free fatty acids) is obtained from the soapstock by acidulation with a mineral acid such as sulfuric or hydrochloric acid. The conventional way of acidulating soapstock is to react it with acid solution at an elevated temperature under continuous agitation. The gummed soapstock typically contains considerable amounts of phospholipids (gums) which act as emulsifiers, for which reason a very long settling time may also be necessary to get acid oil of acceptable purity. If the acidulated soapstock is allowed to settle, it separates into three layers. The bottom layer is an acidic aqueous solution which can be pumped off and recycled. The top layer is the desired fatty acid product, known as acid oil, which may be used as is (e.g., for animal feed), or may be further treated to obtain more highly purified fatty acids (e.g., by distillation). The middle layer is an emulsified sludge material, a semisolid, emulsified layer containing primarily phospholipids, water, and a substantial quantity of the desired fatty acid product entrained therein. With the soapstock containing large amounts of gums and impurities it is often difficult to obtain a complete separation of the phases and may give rise to considerable amount of emulsion layer resulting in significant loss of the acid oil. Also, due to the corrosive nature of the sulfuric acid and the acidulated water the necessary protection against the corrosion make relatively simple equipment rather expensive and the maintenance costs are often considerable.
As a consequence of the foregoing situation, there has existed a longstanding need for a new and improved method of processing crude vegetable oils and the provision of such a method is a stated objective of the present invention.